Reactive coatings comprising an acid-functional compound, an anhydride-functional compound, an epoxy-functional compound and a hydroxy-functional compound

ABSTRACT

Curable compositions which comprise: 
     (i) an acid-functional compound having an average of at least two carboxylic acid groups per molecule; and 
     (ii) an anhydride-functional compound having an average of at least two cyclic carboxylic acid anhydride groups per molecule; and 
     (iii) an epoxy-functional compound having an average of at least one epoxy group per molecule; and 
     (iv) a hydroxy-functional compound having an average of at least two hydroxyl groups per molecule; 
     wherein at least one of the compounds (i), (ii), (iii) or (iv) comprises a film forming polymer.

This is a continuation of application Ser. No. 07/412,355 filed on Aug. 25, 1989, now U.S. Pat. No. 5,043,220, which application was a Divisional of prior application Ser. No. 120,888, filed Nov. 16, 1987, now U.S. Pat. No. 4,871,806 issued Oct. 3, 1989.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel reactive coatings which can be cured at room temperature or force dried at temperatures ranging up to about 350° F. The coatings may be utilized as primers, topcoats or as clearcoats and/or basecoats in clearcoat/basecoat compositions. The combination of carboxylic acid-functional compounds, anhydride-functional compounds, epoxy-functional compounds and hydroxy-functional compounds provides fast reacting, durable coatings which minimize the toxicity problems which may be associated with other low temperature curing systems.

2. Description of the Prior Art

One common prior art approach to high performance low temperature curing coatings has involved two-component coatings comprising reactive isocyanates and active hydrogen-containing compounds such as hydroxyl-containing polymers or amine-containing polymers to produce polyurethane or polyurea coatings. Although these materials have excellent performance and cure at low temperatures, the isocyanates may, under some conditions, be relatively hazardous to handle.

Coating compositions comprising reactive combinations of epoxy-containing compounds and compounds having acid or amine functionality are known in the art. Similarly, coating compositions comprising cyclic anhydrides and hydroxy-functional compounds are also known in the art. The prior art has not, however, taught the combination of anhydride-functional compounds, acid-functional compounds, epoxy-functional compounds and hydroxy-functional compounds to provide low temperature curing coatings having excellent durability and performance.

BRIEF SUMMARY OF THE INVENTION

This invention involves a curable composition which comprises: (i) an acid-functional compound having an average of at least two carboxylic acid groups per molecule; and (ii) an anhydride-functional compound having an average of at least two cyclic carboxylic acid anhydride groups per molecule; and (iii) an epoxy-functional compound having an average of at least one epoxy group per molecule; and (iv) a hydroxy-functional compound having an average of at least two hydroxyl groups per molecule; wherein at least one of the compounds (i), (ii), (iii) or (iv) comprises a film forming polymer. The term "compound" is used in its broadest sense to include monomers, oligomers and polymers. The term "film forming polymer" means any polymeric material that can form a film from evaporation of any carrier or solvent.

In its most preferred formulation, this invention relates to curable compositions wherein the acid-functional compound is a polymer obtained by the half-ester reaction of a hydroxy-functional polymer with a cyclic carboxylic acid anhydride, and wherein the anhydride-functional compound is the free radical addition polymerization product of at least one unsaturated monomer having anhydride functionality and at least one other ethylenically unsaturated monomer, and wherein the epoxy-functional compound is an epoxy compound having an average of at least two epoxy groups per molecule, and wherein the hydroxy-functional compound is the addition polymerization reaction product of at least one unsaturated monomer having hydroxy functionality and at least one other ethylenically unsaturated monomer.

It is especially preferred to utilize the curable composition of this invention in combination with about 5 to about 80% by weight of an inert solvent. It is convenient to provide the coating composition as a multicomponent system which is reactive upon mixing the components. Especially preferred is a two-component system wherein the anhydride-functional compound and the acid-functional compound are combined in one package and the epoxy-functional compound and the hydroxy-functional compound provide a second package. The two packages can then be mixed together to provide the curable coatings immediately prior to application.

In one preferred application, this invention relates to coated substrates having a multi-layer decorative and/or protective coating which comprises:

(a) a basecoat comprising a pigmented film-forming polymer; and

(b) a transparent clearcoat comprising a film-forming polymer applied to the surface of the basecoat composition;

wherein the clearcoat and/or the basecoat comprises the curable compositions of this invention.

Accordingly, it is an object of this invention to provide improved curable compositions having excellent reactivity at low temperatures. It is a further object of this invention to provide coating compositions which may be utilized as primers, topcoats or clearcoats and/or basecoats in clearcoat/basecoat compositions. Another object of this invention is to provide an improved two-package coating composition wherein one package comprises an anhydride-functional compound and an acid-functional compound and the other package comprises an epoxy-functional compound and a hydroxy-functional compound. Another object of this invention is to provide coatings having excellent exterior durability and corrosion resistance. A further object of this invention is to provide improved coating compositions which can be cured at room temperature or force dried at elevated temperatures. These and other objects of the invention will become apparent from the following discussions.

DETAILED DESCRIPTION OF THE INVENTION 1. Acid-Functional Compounds

The acid-functional compounds which are useful in the practice of this invention should have an average of at least two, and preferably at least three, carboxylic acid groups per molecule. Although low molecular weight diacids and polyacids such as phthalic acid, succinic acid, adipic acid, azelaic acid, maleic acid, fumaric acid, trimellitic acid and trimesic acid can be utilized in the practice of this invention, it is especially preferred to utilize polymeric acid-functional compounds.

Preferably the acid-functional polymer will have a number average molecular weight of at least about 400. Typical number average molecular weights of the carboxylic acid-functional polymers will range from about 500 to about 30,000. Representative acid-functional polymers include acrylics, polyesters and polymers prepared by the reaction of anhydrides with hydroxy-functional polymers as discussed more fully below.

1. A. Carboxylic Acid-functional Polymers Prepared by the Half-Ester Forming Reaction of Anhydrides and Hydroxy-Functional Polymers

Especially preferred in the practice of this invention are carboxylic acid-functional polymers prepared by the half-ester reaction of cyclic carboxylic acid anhydrides and hydroxy-functional polymers. The half-ester reaction involves the ring opening of the cyclic anhydride by reaction with a hydroxyl group on the hydroxy-functional polymer to form one ester group and one acid group.

Typically, the hydroxy-functional polymers will have number average molecular weights of at least about 400 and typical number average molecular weights will range from about 400 to about 30,000, and especially 1,000 to about 15,000. Methods of preparing hydroxy-functional polymers are well known in the art and the method of preparation of the hydroxy-functional molecule or polymer is not critical to the practice of this invention. Representative polymers which can be reacted with anhydrides to produce the acid-functional polymers include the hydroxy-functional polyethers, polyesters, acrylics, polyurethanes, poly-caprolactones, etc. as generally discussed in Sections 1.A.1. through 1.A.5. below.

1.A.1.

Polyether polyols are well known in the art and are conveniently prepared by the reaction of a diol or polyol with the corresponding alkylene oxide. These materials are commercially available and may be prepared by a known process such as, for example, the processes described in Encyclopedia of Chemical Technology, Volume 7, pages 257-262, published by Interscience Publishers, Inc., 1951. Representative examples include the polypropylene ether glycols and polyethylene ether glycols such as those marketed as Niax® Polyols from Union Carbide Corporation.

1.A.2.

Another useful class of hydroxy-functional polymers are those prepared by condensation polymerization reaction techniques as are well known in the art. Representative condensation polymerization reactions include polyesters prepared by the condensation of polyhydric alcohols and polycarboxylic acids or anhydrides, with or without the inclusion of drying oil, semi-drying oil, or non-drying oil fatty acids. By adjusting the stoichiometry of the alcohols and the acids while maintaining an excess of hydroxyl groups, hydroxy-functional polyesters can be readily produced to provide a wide range of desired molecular weights and performance characteristics.

The polyester polyols are derived from one or more aromatic and/or aliphatic polycarboxylic acids, the anhydrides thereof, and one or more aliphatic and/or aromatic polyols. The carboxylic acids include the saturated and unsaturated polycarboxylic acids and the derivatives thereof, such as maleic acid, fumaric acid, succinic acid, adipic acid, azelaic acid, and dicyclopentadiene dicarboxylic acid. The carboxylic acids also include the aromatic polycarboxylic acids, such as phthalic acid, isophthalic acid, terephthalic acid, etc. Anhydrides such as maleic anhydride, phthalic anhydride, trimellitic anhydride, or Nadic Methyl Anhydride (brand name for methylbtcyclo[2.2.1]heptene-2,3-dicarboxylic anhydride isomers) can also be used.

Representative saturated and unsaturated polyols which can be reacted in stoichiometric excess with the carboxylic acids to produce hydroxy-functional polyesters include diols such as ethylene glycol, dipropylene glycol, 2,2,4-trimethyl 1,3-pentanediol, neopentyl glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4bis(2-hydroxyethoxy)cyclohexane, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, norbornylene glycol, 1,4-benzenedimethanol, 1,4-benzenediethanol, 2,4-dimethyl-2-ethylenehexane-1,3-diol, 2-butene-1,4-diol, and polyols such as trimethylolethane, trimethylolpropane, trimethylolhexane, triethylolpropane, 1,2,4-butanetriol, glycerol, pentaerythritol, dipentaerythritol, etc.

Typically, the reaction between the polyols and the polycarboxylic acids is conducted at about 120° C. to about 200° C. in the presence of an esterification catalyst such as dibutyl tin oxide.

1.A.3.

Additionally, hydroxy-functional polymers can be prepared by the ring opening reaction of epoxides and/or polyepoxides with primary or, preferably, secondary amines or polyamines to produce hydroxy-functional polymers. Representative amines and polyamines include ethanol amine, N-methylethanol amine, dimethyl amine, ethylene diamine, isophorone diamine, etc. Representative polyepoxides include those prepared by condensing a polyhydric alcohol or polyhydric phenol with an epihalohydrin, such as epichlorohydrin, usually under alkaline conditions. Some of these condensation products are available commercially under the designations EPON or DRH from Shell Chemical Company, and methods of preparation are representatively taught in U.S. Pat Nos. 2,592,560; 2,582,985 and 2,694,694.

1.A.4.

Other useful hydroxy-functional polymers can be prepared by the reaction of an excess of at least one polyol, such as those representatively described in Section 1.A.2 above, with polyisocyanates to produce hydroxy-functional urethanes. Representative polyisocyanates having two or more isocyanate groups per molecule include the aliphatic compounds such as ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene, 2,3-butylene, 1,3-butylene, ethylidene and butylidene diisocyanates; the cycloalkylene compounds such as 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate, and the 1,3-cyclopentane, 1,3-cyclohexane, and 1,2-cyclohexane diisocyanates; the aromatic compounds such as m-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene and 1,4-naphthalene diisocyanates; the aliphatic-aromatic compounds such as 4,4'-diphenylene methane, 2,4- or 2,6-toluene, or mixtures thereof, 4,4'-toluidine, and 1,4-xylylene diisocyanates; the nuclear substituted aromatic compounds such as dianisidine diisocyanate, 4,4'-diphenylether diisocyanate and chlorophenylene diisocyanate; the triisocyanates such as triphenyl methane-4,4',4"-triisocyanate, 1,3,5-triisocyanate benzene and 2,4,6-triisocyanate toluene; and the tetraisocyanates such as 4,4'-diphenyl-dimethyl methane-2,2'-5,5'-tetraisocyanate; the polymerized polyisocyanates such as tolylene diisocyanate dimers and trimers, and other various polyisocyanates containing biuret, urethane, and/or allophanate linkages. The polyisocyanates and the polyols are typically reacted at temperatures of 25° C. to about 150° C. to form the hydroxy-functional polymers.

1.A.5.

Useful hydroxy-functional polymers can also be conveniently prepared by free radical polymerization techniques such as in the production of acrylic resins. The polymers are typically prepared by the addition polymerization of one or more monomers. At least one of the monomers will contain, or can be reacted to produce, a reactive hydroxyl group. Representative hydroxy-functional monomers include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxybutyl acrylate, 4-hydroxypentyl acrylate, 2-hydroxyethyl ethacrylate, 3-hydroxybutyl methacrylate, 2-hydroxyethyl chloroacrylate, diethylene glycol methacrylate, tetraethylene glycol acrylate, para-vinyl benzyl alcohol, etc. Typically the hydroxy-functional monomers would be copolymerized with one or more monomers having ethylenic unsaturation such as:

(i) esters of acrylic, methacrylic, crotonic, tiglic, or other unsaturated acids such as: methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, amyl acrylate, 3,5,5-trimethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, dimethylaminoethyl methacrylate, isobornyl methacrylate, ethyl tiglate, methyl crotonate, ethyl crotonate, etc.;

(ii) vinyl compounds such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl benzoate, vinyl m-chlorobenzoate, vinyl p-methoxybenzoate, vinyl alpha-chloroacetate, vinyl toluene, vinyl chloride, etc.;

(iii) styrene-based materials such as styrene, alpha-methyl styrene, alpha-ethyl styrene, alpha-bromo styrene, 2,6-dichlorostyrene, etc.;

(iv) allyl compounds such as allyl chloride, allyl acetate, allyl benzoate, allyl methacrylate, etc.;

(v) other copolymerizable unsaturated monomers such as ethylene, acrylonitrile, methacrylonitrile, dimethyl maleate, isopropenyl acetate, isopropenyl isobutyrate, acrylamide, methacrylamide, and dienes such as 1,3-butadiene, etc.

The polymers are conveniently prepared by conventional free radical addition polymerization techniques. Frequently, the polymerization will be catalyzed by conventional catalysts known in the art to generate a free radical such as azobis(isobutyronitrile), cumene hydroperoxide, t-butyl perbenzoate, etc. Typically, the acrylic monomers are, heated in the presence of the catalyst at temperatures ranging from about 35° C. to about 200° C., and especially 75° C. to 150° C., to effect the polymerization. The molecular weight of the polymer can be controlled, if desired, by the monomer selection, reaction temperature and time, and/or the use of chain transfer agents as is well known in the art.

Especially preferred polymers in the practice of this invention for reaction with the cyclic anhydride to produce the carboxylic acid-functional polymers are hydroxy-functional polyesters and hydroxy-functional acrylic polymers. An especially preferred hydroxy-functional polymer is the addition polymerization reaction product of (a) 5 to 100, and especially 10 to about 40, weight percent of a hydroxy-functional ethylenically unsaturated monomer and (b) 0 to 95, and especially 60 to about 90, weight percent of at least one other ethylenically unsaturated monomer copolymerizable with the hydroxy-functional monomer.

The cyclic carboxylic acid anhydrides useful in the practice of this invention to produce the carboxylic acid-functional half-ester product by reaction with the hydroxy-functional compound can be any monomeric aliphatic or aromatic cyclic anhydride having one anhydride group per molecule. Representative anhydrides include, phthalic anhydride, 3-nitrophthalic. anhydride, 4-nitrophthalic anhydride, 3-flourophthalic anhydride, 4-chlorophthalic anhydride, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, succinic anhydride, dodecenylsuccinic anhydride, octylsuccinic anhydride, maleic anhydride, dichloromaleic anhydride, glutaric anhydride, adipic anhydride, chlorendic anhydride, itaconic anhydride, citraconic anhydride, endo-methylenetetrahydrophthalic anhydride, cyclohexane-1,2-dicarboxylic anhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 4-methyl-4-cyclohexene-1,2-dicarboxylic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, 1,4-cyclohexadiene-1,2-dicarboxylic anhydride, 1,3-cyclopentanedicarboxylic anhydride, diglycolic acid anhydride, etc. Maleic anhydride is especially preferred because of its reactivity and relatively low cost. Other useful anhydrides include those anhydrides having a free carboxyl group in addition to the anhydride group such as trimellitic anhydride, aconitic anhydride, 2,6,7-naphthalene tricarboxylic anhydride, 1,2,4-butane tricarboxylic anhydride, 1,3,4-cyclopentane tricarboxylic anhydride, etc.

The reaction of the hydroxy-functional compound and the cyclic anhydride should normally be conducted at temperatures less than about 75° C., preferably less than 65° C., and most preferably between about 35° C. to 60° C. The reaction temperature is maintained until the reaction has proceeded to provide the desired amount of half-ester groups on the acid-functional compound. Normally, as a convenient measure of the extent of the reaction, the reaction will be continued until no change in the amount of residual unreacted anhydride can be observed, and will generally involve reacting at least about 70%, and preferably at least 95%, of the available anhydride. If the subsequent end use of the acid-functional polymer can tolerate the remaining free anhydride, if any, no separation or removal of the excess unreacted anhydride is necessary. If the end use of the acid-functional polymer requires that it be free of any unreacted anhydride, the reaction can be continued until substantially all of the anhydride has reacted, or the free anhydride may be removed by vacuum distillation or other techniques well known in the art.

The level of anhydride reacted with the hydroxy-functional compound need only be sufficient to provide the final desired acid value of the acid functional compound. Typically the reaction would be conducted by admixing the polyol and the anhydride at levels to provide at least about 0.3 and normally about 0.7 to 1.0 anhydride groups for each hydroxyl group. By conducting the reaction at temperatures less than about 75° C. the carboxylic acid groups formed as part of the half-ester are not appreciably reactive with the hydroxyl groups themselves and so they do not compete with the ring opening half-ester reaction of the remaining anhydrides.

In order to conduct the reaction at these relatively low temperatures, it is preferred to utilize an esterification catalyst. The catalyst should be present in sufficient amount to catalyze the reaction and typically will be present at a level of at least about 0.01%, and normally from about 0.05% to about 3.0%, based upon the weight of the cyclic anhydride. Catalysts which are useful in the esterification reaction of the anhydride with the hydroxy-functional molecule include mineral acids such as hydrochloric acid and sulfuric acid; alkali metal hydroxides such as sodium hydroxide; tin compounds such as stannous octoate, or dibutyltin oxide; aliphatic or aromatic amines, especially tertiary alkyl amines, such as triethylamine; and aromatic heterocyclic amines such as N-methyl imidazole and the like. Especially preferred are N-methyl imidazole and triethylamine.

Although the reaction between the hydroxy-functional compound and the anhydride can be conducted in the absence of solvent if the materials are liquid at the reaction temperature, it is normally preferred to conduct the reaction in the presence of an inert solvent such as esters, ketones, ethers or aromatic hydrocarbons. If desired, the acid-functional molecule can be utilized as the solvent solution, or, optionally, all or part of the inert solvent may be removed, e.g. by distillation, after the reaction is completed.

After the reaction is completed, it is frequently desirable to add a low molecular weight alcohol solvent, such as isobutanol or isopropanol, to the acid-functional at a level of about 5 to 35 percent by weight to provide stabilization on storage.

1.B

Carboxylic Acid-Functional Polymers Prepared From Unsaturated Acid-Functional Monomers.

Useful acid-functional polymers can also be conveniently prepared by addition polymerization techniques such as in the production of acrylic resins. The acid-functional polymers are routinely prepared by the free radical addition polymerization of unsaturated acids such as maleic acid, acrylic acid, methacrylic acid, crotonic acid, etc. along with one or more unsaturated monomers. Representative monomers include the esters of unsaturated acids, vinyl compounds, styrene-based materials, allyl compounds and other copolymerizable monomers as representatively taught in Section 1.A.5. of this specification. The monomers which are co-polymerized with the unsaturated acid should be free of any functionality which could react with the acid groups during the polymerization.

1.C

Carboxylic Acid-Functional Polymers Prepared From Polyols and Polyacids

Other useful acid-functional polymers include polyester polymers obtained from the reaction of one or more aromatic and/or aliphatic carboxylic acids or their anhydrides and one or more aliphatic and/or aromatic polyols wherein the acid functionality is present in a stoichiometric excess over the hydroxy functionality. Representative carboxylic acids and polyols include those listed in Section 1.A.2. of this specification.

2. Anhydride-Functional Compounds

The anhydride-functional compounds which are useful in the practice of this invention can be any aliphatic or aromatic compound having at least two cyclic carboxylic acid anhydride groups in the molecule. Polymeric anhydrides having number average molecular weights between 500 and 7,000 are most useful. Especially preferred in the practice of this invention is the use of free radical addition polymers, such as acrylic polymers, having anhydride functionality. These are conveniently prepared as is well known in the art by the polymerization under free radical addition polymerization conditions of at least one unsaturated monomer having anhydride functionality, such as maleic anhydride, citraconic anhydride, itaconic anhydride, propenyl succinic anhydride, etc. optionally with other ethylenically unsaturated monomers such as the esters of unsaturated acids, vinyl compounds, styrene-based materials, allyl compounds and other copolymerizable monomers, all as representatively taught in Section 1.A.5. of this specification. The monomers which are copolymerized with the unsaturated anhydride should, of course, be free of any functionality which could react with the anhydride group during the polymerization. The anhydride-functional polymers can be conveniently prepared by conventional free radical addition polymerization techniques. Typically the polymerization will be conducted in an inert solvent and in the presence of a catalyst at temperatures ranging from 35° C. to about 200° C. The anhydride-functional polymers should comprise at least 5% by weight of the anhydride. An especially preferred anhydride-functional free radical addition polymer comprises the free radical addition polymerization product of (a) 5 to 40, and especially 15 to about 25, weight percent of an ethylenically unsaturated monoanhydride and (b) 60 to 95, and especially 75 to about 85, weight percent of at least one other ethylenically unsaturated monomer copolymerizable with the ethylenically unsaturated anhydride.

Other polyanhydrides, in addition to the acrylic polymeric anhydrides prepared by a free radical addition process, can also be utilized in the practice of this invention. Ester anhydrides can be prepared, as is known in the art, by the reaction of e.g. trimellitic anhydride with polyols. Other representative, suitable polyanhydrides include poly-functional cyclic dianhydrides such as cyclopentane tetracarboxylic acid dianhydride, diphenyl-ether tetracarboxylic acid dianhydride, 1,2,3,4,-butane tetracarboxylic acid dianhydride, and the benzophenone tetracarboxylic dianhydrides such as 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 2,bromo-3,3',4,4'-benzophenone tetracarboxylic acid dianhydride. Trianhydrides such as the benzene and cyclohexene hexacarboxylic acid trianhydrides are also useful.

Additionally, useful polyanhydrides can be prepared by the maleinization of polyunsaturated compounds such as unsaturated rubbers, unsaturated oils and unsaturated hydrocarbons.

3. Epoxy-Functional Compounds

The coatings of this invention also require the use of at least one epoxy-functional compound. The epoxy compounds can be monoepoxides or, preferably, a polyepoxide having an average of at least two epoxy groups per molecule.

Representative useful monoepoxides include the monoglycidyl ethers of aliphatic or aromatic alcohols such as butyl glycidyl ether, octyl glycidyl ether, nonyl glycidyl ether, decyl glycidyl ether, dodecyl glycidyl ether, p-tert-butylphenyl glycidyl ether, and o-cresyl glycidyl ether. Monoepoxy esters such as the glycidyl ester of versatic acid (commercially available as CARDURA® E from Shell Chemical Company), or the glycidyl esters of other acids such as tertiary-nonanoic acid, tertiary-decanoic acid, tertiary-undecanoic acid, etc. are also useful. Similarly, if desired, unsaturated monoepoxy esters such as glycidyl acrylate, glycidyl methacrylate or glycidyl laurate could be used. Additionally, monoepoxidized oils can also be used.

Other useful monoepoxides include styrene oxide, cyclohexene oxide, 1,2-butene oxide, 2,3-butene oxide, 1,2-pentene oxide, 1,2-heptene oxide, 1,2-octene oxide, 1,2-nonene oxide, 1,2-decene oxide, and the like.

It is only necessary that the monoepoxide compounds have a sufficiently low volatility to remain in the coating composition under the applicable conditions of cure.

Polyepoxides are especially preferred in the reactive coatings of this invention. Especially preferred as the polyepoxides due to their reactivity and durability, are the cycloaliphatic polyepoxides. Preferably, the cycloaliphatic polyepoxides will have a number average molecular weight less than about 2,000 to minimize the viscosity. The cycloaliphatic polyepoxides are conveniently prepared by methods well known in the art such as epoxidation of dienes or polyenes, or the epoxidation of unsaturated esters by reaction with a peracid such as peracetic and/or performic acid.

Commercial examples of representative preferred cycloaliphatic polyepxides include 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate (e.g. "ERL-4221" from Union Carbide Corp.); bis(3,4-epoxycyclohexylmethyl)adipate (e.g. "ERL-4299" from Union Carbide Corporation); 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexane carboxylate (e.g. "ERL-4201" from Union Carbide Corp. ); bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate (e.g. "ERL-4289" from Union Carbide Corp. ); bis(2,3-epoxycyclopentyl) ether (e.g. "ERL-0400" from Union Carbide Corp.); dipentene dioxide (e.g. "ERL-4269" from Union Carbide Corp.); 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-metadioxane (e.g. "ERL-4234" from Union Carbide Corp.). Other commercially available cycloaliphatic polyepoxides are available from Ciba-Geigy Corporation such as CY 192, a cycloaliphatic diglycidyl ester epoxy resin having an epoxy equivalent weight of about 154. The manufacture of representative cycloaliphatic polyepoxides is taught in various patents including U.S. Pat. Nos. 2,884,408, 3,027,357 and 3,247,144.

Other polyepoxides potentially useful in the practices of this invention include aliphatic and aromatic polyepoxides, such as those prepared by the reaction of an aliphatic polyol or polyhydric phenol and an epihalohydrin. Other useful polyepoxides include epoxidized oils and acrylic polymers derived from ethylenically unsaturated epoxy-functional monomers such as glycidyl acrylate or glycidyl methacrylate in combination with other copolymerizable monomers such as those listed in 1.A.5 above.

4. Hydroxy-Functional Compounds

The hydroxy-functional compounds which are useful in the practice of this invention should have an average of at least two hydroxyl groups per molecule. Although low molecular weight diols and polyols such as propylene glycol, 1,6-hexanediol, triethanol amine and pentaerythritol can be utilized in the practice of this invention, it is especially preferred to utilize polymeric hydroxy-functional compounds such as polyethers, polyesters, acrylics, polyurethanes, polycaprolactones, etc.

Preferably the hydroxy-functional polymer will have a number average molecular weight of at least about 400. Typical number average molecular weights will range from about 400 to about 30,000, and especially 1,000 to about 15,000. In order to provide the fastest rate of reaction during cure it is preferred in the practice of this invention to utilize hydroxy-functional compounds having predominantly, and preferably all, primary hydroxy functionality.

Representative hydroxy-functional polymers are taught in Sections 1.A.1. through 1.A.5. of this specification. Especially preferred as the hydroxy-functional polymer is a hydroxy-functional polymer comprising the addition polymerization of (a) 10 to about 60 weight percent of a hydroxy-functional ethylenically unsaturated monomer and (b) 40 to about 90 weight percent of at least one ethylenically unsaturated monomer copolymerizable with the hydroxy-functional monomer.

The ratios of anhydride to acid to epoxy to hydroxyl groups can be widely varied within the practice of this invention as long as at least some of each group is present in the reactive coating. It is preferred, however, to provide about 0.05 to about 3.0 acid groups and about 0.5 to about 4.0 epoxy groups and about 0.05 to 6.0 hydroxyl groups for each anhydride group in the reactive system. It is especially preferred to provide 1.0 to about 2.0 acid groups and 1.0 to about 3.0 epoxy groups and about 1.0 to about 4.0 hydroxyl groups for each anhydride group.

At least one of the hydroxy-functional compound, the acid-functional compound, the epoxy-functional compound, or the anhydride-functional compound should be a film-forming polymer, and each of the compounds should be mutually soluble with the other compounds. If desired, more than one of any of the acid-functional, anhydride-functional, epoxy-functional or hydroxy-functional compounds could be utilized in a single coating formulation.

The coatings of this invention can be cured at temperatures ranging from about room temperature up to about 350° F. The coatings can be used as clear coatings or they may contain pigments as is well known in the art. Representative opacifying pigments include white pigments such as titanium dioxide, zinc oxide, antimony oxide, etc. and organic or inorganic chromatic pigments such as iron oxide, carbon black, phthalocyanine blue, etc. The coatings may also contain extender pigments such as calcium carbonate, clay, silica, talc, etc.

The coatings may also contain other additives such as flow agents, catalysts, diluents, solvents, ultraviolet light absorbers, etc.

It is especially preferred in the practice of this invention to include a catalyst for the reaction of anhydride groups and hydroxyl groups and also a catalyst for the reaction of epoxy and acid groups. It is especially preferred in the practice of this invention to utilize tertiary amines and especially N-methylimidazole as a catalyst for the anhydride/hydroxyl reaction. The catalyst for the anhydride/hydroxyl reaction will typically be present at a level of at least 0.01% by weight of the anhydride compound and preferably 1.0 to about 5.0%.

Tertiary amines, secondary amines such as ethyl imidazole, quaternary ammonium salts, nucleophilic catalysts, such as lithium iodide, phosphonium salts, and phosphines such as triphenyl phosphine are especially useful as catalysts for epoxy/acid reactions. The catalyst for the epoxy/acid reaction will typically be present at a level of at least 0.01% by weight of the total acid-functional compound and epoxy-functional compound and will be present at 0.1 to about 3.0%.

Since the curable compositions of this invention are typically provided as multi-package systems which must be mixed together prior to use, the pigments, catalysts and other additives can be conveniently added to any or all of the individual packages.

The coatings of this invention may typically be applied to any substrate such metal, plastic, wood, glass, synthetic fibers, etc. by brushing, dipping, roll coating, flow coating, spraying or other method conventionally employed in the coating industry.

One preferred application of the curable coatings of this invention relates to their use as clearcoats and/or basecoats in clearcoat/basecoat formulations.

Clearcoat/basecoat systems are well known, especially in the automobile industry where it is especially useful to apply a pigmented basecoat, which may contain metallic pigments, to a substrate and allow it to form a polymer film followed by the application of a clearcoat which will not mix with or have any appreciable solvent attack upon the previously applied basecoat. The basecoat composition may be any of the polymers known to be useful in coating compositions including the reactive compositions of this invention.

One useful polymer basecoat includes the acrylic addition polymers, particularly polymers or copolymers of one or more alkyl esters of acrylic acid or methacrylic acid, optionally together with one or more other ethylenically unsaturated monomers. These polymers may be of either the thermoplastic type or the thermosetting, crosslinking type which contain hydroxyl or amine or other reactive functionality which can be crosslinked. Suitable acrylic esters for either type of polymer include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, vinyl acetate, acrylonitrile, acrylamide, etc. Where the polymers are required to be of the crosslinking type, suitable functional monomers which can be used in addition to those already mentioned include acrylic or methacrylic acid, hydroxy ethyl acrylate, 2-hydroxy propyl methacrylate, glycidyl acrylate, tertiary-butyl amino ethyl methacrylate, etc. The basecoat composition may, in such a case, also contain a crosslinking agent such as a polyisocyanate a polyepoxide, or a nitrogen resin such as a condensate of an aldehyde such as formaldehyde with a nitrogeneous compound such as urea, melamine or benzoguanamine or a lower alkyl ether of such a condensate. Other polymers useful in the basecoat composition include vinyl copolymers such as copolymers of vinyl esters of inorganic or organic acids, such as vinyl chloride, vinyl acetate, vinyl propionate, etc., which copolymers may optionally be partially hydrolyzed so as to introduce vinyl alcohol units.

Other polymers useful in the manufacture of the basecoat include alkyd resins or polyesters which can be prepared in a known manner by the condensation of polyhydric alcohols and polycarboxylic acids, with or without the inclusion of natural drying oil fatty acids as described elsewhere in this specification. The polyesters or alkyds may contain a proportion of free hydroxyl and/or carboxyl groups which are available for reaction, if desired with suitable crosslinking agents as discussed above.

If desired, the basecoat composition may also contain minor amounts of a cellulose ester, to alter the drying or viscosity characteristics of the basecoat.

Typically, the basecoat will include pigments conventionally used for coating compositions and after being applied to a substrate, which may or may not previously have been primed, the basecoat will be allowed sufficient time to form a polymer film which will not be lifted during the application of the clearcoat. The clearcoat is then applied to the surface of the basecoat, and the system can be allowed to dry or, if desired, can be force dried by baking the coated substrate at temperatures typically ranging up to about 250° F.

Typically, the clearcoat may contain ultraviolet light absorbers suck as hindered phenols or hindered amines at a level ranging up to about 6% by weight of the vehicle solids as is well known in the art. The clearcoat can be applied by any application method known in the art, but preferably will be spray applied. If desired, multiple layers of basecoat and/or clearcoat can be applied. Typically, both the basecoat and the clearcoat will each be applied to give a dry film thickness of about 0.01 to about 6.0, and especially about 0.5 to about 3.0 mils.

The following examples have been selected to illustrate specific embodiments and practices of advantage to a more complete understanding of the invention. Unless otherwise stated, "parts" means parts-by-weight and "percent" is percent-by-weight. The numeric ratings for solvent resistance (MEK rubs), wet adhesion, and salt spray are on a scale of 0-10, 10 best.

In each of the clearcoat/basecoat formulations described in Examples 6 through 15 the primer was G.B.P.® etching primer filler (2-component vinyl-butyral based primer commercially available from The Sherwin-Williams Company) and the basecoat was Acrylyd® acrylic enamel (a lacquer-like coating commercially available from The Sherwin-Williams Company). The primer, the basecoat and the clearcoat were applied to provide dry film thicknesses of 1.0, 1.0 and 2.0 mils respectively.

EXAMPLE 1 Preparation of Anhydride-Functional Acrylic Polymer

A 4 neck, round bottomed flask equipped with mechanical stirrer, reflux condenser, thermometer, nitrogen inlet and fluid metering pump was charged with 1472 parts xylene, 240 parts maleic anhydride and heated to reflux (139° C.) under nitrogen. A monomer mixture of 480 parts isobutyl methacrylate, 720 parts butyl acrylate, 720 parts methyl methacrylate, 120 parts maleic anhydride and 60 parts t-butyl perbenzoate were then metered into the reaction over a 3-hour period. Halfway through the addition, an additional 120 parts of maleic anhydride was charged to the reaction vessel and monomer addition was continued. After refluxing the reaction mixture for an additional 15 minutes, 12 parts of t-butyl perbenzoate in 128 parts xylene were added over 45 minutes. Heating was continued for 2 hours at reflux. The resulting xylene soluble anhydride-functional resin was 61.2% solids, had a Gardner Holdt viscosity of 24.5, an acid-value of 116.5, and a density of approximately 8.6 pounds per gallon.

EXAMPLE 2 Carboxy-Functional Acrylic Polymer

A carboxy-functional acrylic polymer was prepared by charging a reaction vessel equipped with a mechanical stirrer, reflux condenser, thermometer, nitrogen inlet and fluid metering pump with 1621.2 parts xylene which was then heated the solvent to 120° C. under nitrogen. A monomer mixture composed of 1013.2 parts hydroxy ethyl acrylate, 1013.2 parts Tone M-100 (trade name of Union Carbide's hydroxy acrylic/caprolactone adduct believed to be the reaction product of 1 mole of hydroxy ethyl acrylate and 2 moles of caprolactone), 2837.2 parts methyl methacrylate, 3242.1 parts isobutyl methacrylate, 81.1 parts Vazo 67 (trademark for E. I. duPont initiator believed to be 2,2'-azobis(2-methylbutyronitrile)) and 6352.9 parts xylene was metered into the reaction vessel over a period of 3 hours while maintaining the temperature of the reaction vessel at 120° C. After the monomer mix addition was completed, the temperature of the reaction mixture was raised to reflux (137° C.) and 20.3 parts Vazo 67 in 131.4 parts xylene was added over a period of 30 minutes. Reflux temperature was maintained for one additional hour. After cooling the reaction mixture to room temperature, 1144.4 parts maleic anhydride and 1144.4 parts xylene were added. The polymeric solution was heated to 60° C. and 10.8 parts triethyl amine was added. The reaction mixture was stirred and maintained at 60° C. for approximately 6 hours. The resulting carboxylic acid-functional acrylic polymer had a theoretical percent solids of 48.1, a Gardner Holdt viscosity of V-, and an acid equivalent weight of 790.

EXAMPLE 3 Hydroxy-Functional Acrylic Polymer

A hydroxy-functional polymer was prepared by initially charging a polymerization reactor equipped with a mechanical stirrer, a water cooled condenser, nitrogen inlet, water trap, thermometer, heating mantle and fluid metering pump with 172.5 parts of n-butyl acetate. The reaction vessel was heated to approximately 237° F. and a monomer premix composed of 96.2 parts of methyl methacrylate, 63.0 parts of butyl acrylate, 58 parts of hydroxy ethyl methacrylate, 54 parts styrene and an initiator premixture composed of 11.5 parts of n-butyl acetate and 5.7 parts of Vazo 67 was metered simultaneously into the polymerization reactor at a constant rate over approximately 4 hours. The reaction temperature was maintained for an additional 2 hours after the addition was completed and cooled for one hour. The resulting hydroxy-functional polymer had a number average molecular weight of approximately 9,600.

EXAMPLE 4 Anhydride-Functional Acrylic Polymer

A reaction vessel equipped as in Example I was charged with 6,624 parts of xylene, 648 parts of maleic anhydride and heated to reflux under nitrogen. To this heated solution a monomer mixture of 5,616 parts butyl acrylate, 3,024 parts methylmethacrylate, 540 parts maleic anhydride and 270 parts of t-butyl peroctoate was metered into the reaction vessel at a constant rate over a 3-hour time period. At 1 hour and at 2 hours into the monomer addition, heating and monomer addition were stopped and the reactor was charged with 540 parts and 432 parts of maleic anhydride respectively. Heating was resumed to reflux and the monomer addition was continued. The reaction mixture was maintained at reflux temperature for an additional 15 minutes after the completion of all of the monomer addition. A solution of 54 parts of t-butyl peroctoate in 576 parts xylene was added to the reaction over a 45-minute period. The reaction was held at reflux for an additional 2 hours and then allowed to cool to room temperature to obtain an anhydride-functional polymer having a number average molecular weight of about 1,800 and a free maleic anhydride content of less than 0.1%. This polymer had an average of about 3.6 anhydride groups per molecule.

EXAMPLE 5 Preparation of Clear Coating

A curable clear coating was prepared according to the following recipe:

    ______________________________________                                         Raw Material         Parts-By-Weight                                           ______________________________________                                         Hydroxyy-Functional Acrylic Resin                                                                   170.31                                                    of Example 3                                                                   ERL 4221.sup.1       54.46                                                     Acid-Funtional Polymer of                                                                           430.84                                                    Example 2                                                                      Xylene               37.56                                                     Toluene              43.44                                                     Byk 300.sup.2        2.5                                                       20% N-Methylimidazole/                                                                              4.78                                                      Methyl Isobutyl Ketone                                                         20% Triphenylphosphine/                                                                             13.19                                                     Toluene                                                                        Tinuvin 292.sup.3    2.95                                                      20% Tinuvin 328.sup.4 /Toluene                                                                      24.59                                                     Anhydride-Functional Polyner of                                                                     44.35                                                     Example 1                                                                      ______________________________________                                          .sup.1 Union Carbide trademark for 3,4epoxycyclohexylmethyl                    3,4epoxycyclohexane carboxylate                                                .sup.2 flow control agent sold by BykMalinkrodt                                .sup.3 trademark of CibaGeigy for di[4(2,2,6,6tetramethyl                      piperdinyl)]sebacate light stabilizer                                          .sup.4 trakemark of CibaGeigy for 2(2-hydroxy-3,5-ditertiary                   amylphenol)-2H-benzotriazole                                             

This coating formulation represented approximately 3.0 hydroxyl groups, about 3.0 epoxy groups and 2.0 carboxylic acid groups for each anhydride group. The triphenylphosphine catalyst was present at approximately 1% on epoxy and carboxylic acid solids, and the N-methylimidazole is present at approximately 3.5% of the anhydride resins solids.

The clear coatings were applied to metal substrates immediately after mixing and allowed to air dry. The coated films exhibited a Konig Pendulum Hardness number of 12 after one day, 45 after seven days and 72 after 35 days. The cured films had good solvent resistance, excellent resistance to humidity (170 hours) and to salt spray (170 hours).

EXAMPLE 6

A curable clear coating intended for use over a basecoat/primer system was prepared according to the following recipe:

    ______________________________________                                         Raw Materials             Parts                                                ______________________________________                                         Carboxylic Acid-Functional Polymer of                                                                    422.72                                               Example 2                                                                      ERL 4221                  53.22                                                Anhydride-Funtional Polymer of Example 1                                                                 44.08                                                Hydroxy-Functional Polymer of Example 3                                                                  163.02                                               Xylene                    108.81                                               Byk 300                   2.5                                                  20% N-Methylimidazole/Methyl Isobutyl Ketone                                                             4.70                                                 20% Tinuvin 328/Toluene   24.05                                                Tinuvin 292               2.89                                                 ______________________________________                                    

This clear formulation represents 3.0 hydroxyl groups, 3.0 epoxy groups and 2.0 carboxylic acid groups per each anhydride group. The N-methylimidazole catalyst is present at about 3.5% based on the anhydride resin solids. This coating was reduced with suitable solvents and spray applied over the primer and basecoat on iron phosphate treated cold rolled steel. The coating system was allowed to ambient cure 24 hours before testing.

The resultant film exhibited a Konig Pendulum Hardness reading of 9 after one day, 21 after one week and 30 after four weeks. The coating exhibited solvent resistance of 2 after one day and 9 after four weeks. A 20° gloss reading of 84 and a distinctness of image reading of 92 was obtained. Salt spray resistance at 170 hours of exposure to 5% salt spray solution was excellent.

EXAMPLES 7-15

Examples 7-15 were carried out by a similar procedure to that described for Example 6 except for the modifications described in the table below. The anhydride-functional polymer used in Examples 7-15 is that described in Example 4.

                                      TABLE 1                                      __________________________________________________________________________     Example   7   8   9   10  11  12  13  14  15                                   __________________________________________________________________________     Acid Resin                                                                               0.111                                                                              0.250                                                                              0.250                                                                              0.167                                                                              0.167                                                                              0.278                                                                              0.278                                                                              0.167                                                                              0.208                                [Equivalent]                                                                             [.48]                                                                              [1] [2.5]                                                                              [.67 ]                                                                             [0.7]                                                                              [1.66]                                                                             [4] [1.67]                                                                             [1.2]                                Epoxy Resin                                                                              0.222                                                                              0.250                                                                              0.250                                                                              0.333                                                                              0.167                                                                              0.389                                                                              0.389                                                                              0.333                                                                              0.292                                [Equivalent]                                                                             [.95]                                                                              [1] [2.5]                                                                              [1.33]                                                                             [.7]                                                                               [2.33]                                                                             [5.8]                                                                              [3.33]                                                                             [1.67]                               Hydroxy Resin                                                                            0.433                                                                              0.250                                                                              0.400                                                                              0.250                                                                              0.433                                                                              0.167                                                                              0.267                                                                              0.400                                                                              0.325                                [Equivalent]                                                                             [1.85]                                                                             [1] [4] [1] [1.85]                                                                             [1] [4] [4] [1.85]                               Anhydride Resin                                                                          0.233                                                                              0.250                                                                              0.100                                                                              0.250                                                                              0.233                                                                              0.167                                                                              0.067                                                                              0.100                                                                              0.175                                [Equivalent]                                                                             [1] [1] [1] [1] [1] [1] [1] [1] [1]                                  KONIG PENDULUM                                                                           41  31  30  40  32  33  32  34  34                                   Hardness (4 weeks)                                                             MEK Rubs (4 weeks)                                                                       7   7   6.5 6   7   8.5 8.5 8   8.5                                  DFT (mils)                                                                               4.0 4.4 4.4 4.3 4.4 4.2 4.2 4.3 4.4                                  20° Gloss                                                                         84  82  82  80  82  84  82  81  82                                   DOI       81  84  83  83  84  92  82  85  80                                   HUMIDITY                                                                       Init Gloss                                                                               81  82  87  82  84  83  84  85  85                                   Final Gloss                                                                              34  37  55  39  42  40  62  52  40                                   % Retention                                                                              42  45  63  48  50  48  74  61  47                                   Wet Adhesion                                                                             5   3   0   5   5   2   5   0   5                                    SALT SPRAY                                                                               6   8   8   9   8   8   8   7   8                                    Scribe Corrosion                                                               __________________________________________________________________________

EXAMPLES 16-19

Examples 16-19 were prepared by mixing the components to provide the equivalent and weight ratios identified in the Table below and applying the coatings to iron phosphate treated cold rolled steel substrates and baking the coated substrates for 30 minutes at 180° F. In the Table below the epoxy compound was ERL-4221, the acid-functional polymer was that of Example 2, the hydroxy-functional polymer was that of Example 3, and the anhydride-functional polymer was that of Example 4.

                  TABLE 2                                                          ______________________________________                                         BAKED EXAMPLES                                                                                16    17      18      19                                        ______________________________________                                         Weight and Equivalent Ratios                                                   Epoxy/COOH Equivalents                                                                          1.5/1   1.4/1   1.5/1 1.5/1                                   OH/ANH Equivalents                                                                              3.0/1   2.0/1   2.5/1 2.5/1                                   % Epoxy/COOH Solids                                                                             67%     50%     90%   10%                                     % OH/ANH Solids  33%     50%     10%   90%                                     RESULTS                                                                        KONIG PENDULUM HARDNESS                                                        1 Day            66      57      54    78                                      1 Week           109     92      114   102                                     4 Weeks          128     111     134   110                                     MEK                                                                            1 Day            3       4       5     7                                       1 Week           4       5       6     7                                       4 Weeks          5       5       6     7                                       20° Gloss 94      92      93    94                                      HUMIDITY                                                                       Wet Adhesion     10      10      10    10                                      Blushing         7       10      10    0                                       Gloss Retention-Post 1 hr                                                                       98%     99%     100%  24%                                     SALT SPRAY                                                                     Scribe Creepage (mm)                                                                            6       4       6     5                                       Scribe Corrosion 6       7       4     4                                       ______________________________________                                    

While this invention has been described by a specific number of embodiments, it is obvious that other variations and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims. 

The invention claimed is:
 1. A curable composition which comprises:(i) an acid-functional polymer having an average of at least two carboxylic acid groups per molecule and which is selected from the group consisting of acid-functional free radical addition polymers obtained by the polymerization of unsaturated acids and one or more copolymerizable monomers, and acid-functional polyester polymers, with the proviso that the acid-functional polymers are not obtained by the reaction of a hydroxy-functional polymer and a cyclic carboxylic acid anhydride; and (ii) an anhydride-functional polymer having an average of at least two cyclic carboxylic acid anhydride groups per molecule, wherein the polymer is the addition polymerization reaction product of at least one unsaturated monomer having anhydride functionality and, optionally, at least one other copolymerizable unsaturated monomer; and (iii) an epoxy-functional compound having an average of at least one epoxy group per molecule; and (iv) a hydroxy-functional compound having an average of at least two hydroxyl groups per molecule;with the proviso that none of the acid-functional polymer (i), the anhydride functional polymer (ii), the epoxy functional compound (iii), or the hydroxy functional compound (iv) are identical to each other.
 2. The composition of claim 1 further characterized in that the acid-functional polymer is an acid-functional polymer having a number average molecular weight of at least about
 400. 3. The composition of claim 1 further characterized in that the anhydride-functional polymer is an anhydride-functional polymer having a number average molecular weight of at least about
 500. 4. The-composition of claim 3 further characterized in that the anhydride-functional polymer is the additon polymerization reaction product of (a) 5 to 40 weight percent of an ethylenically unsaturated monoanhydride and (b) 60 to 95 weight percent of at least one other ethylenically unsaturated monomer copolymerizable with the ethylenically unsaturated anhydride.
 5. The composition of claim 4 further characterized in that the monoanhydride is maleic anhydride.
 6. The composition of claim 1 further characterized in that the epoxy-functional compound has an average of at least two epoxy groups per molecule.
 7. The composition of claim 6 further characterized in that the epoxy-functional compound is a cycloaliphatic polyepoxide.
 8. The composition of claim 7 further characterized in that the cycloaliphatic polyepoxide is selected from the group consisting of 3,4-epoxy cyclohexylmethyl 3,4-epoxycyclohexane carboxylate; 3,4-epoxy 6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexane carboxylate; bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate; bis (2,3-epoxycyclopentyl) ether; dipentene dioxide; 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-metadioxane; and bis(3,4-epoxycyclohexylmethyl)adipate.
 9. The composition of claim 1 further characterized in that the hydroxy-functional compound is a hydroxy-functional polymer having a number average molecular weight of at least about
 400. 10. The composition of claim 9 further characterized in that the hydroxy-functional polymer is selected from the group consisting of hydroxy-functional polyethers, polyesters, acrylic polymers, polyurethanes, and polycaprolactones.
 11. The composition of claim 9 further characterized in that the hydroxy-functional polymer is the addition polymerization reaction product of (a) 10 to about 60 weight percent of a hydroxy-functional ethylenically unsaturated monomer and (b) 40 to about 90 weight percent of at least one ethylenically unsaturated monomer copolymerizable with the hydroxy-functional monomer.
 12. The composition of claim 1 further characterized in that it also incorporates a catalyst for the reaction of acid groups and epoxy groups.
 13. The composition of claim 12 further characterized in that the catalyst is triphenyl phosphine.
 14. The composition of claim 1 further characterized in that it also incorporates a catalyst for the reaction of anhydride and hydroxyl groups.
 15. The composition of claim 14 further characterized in that the catalyst is a tertiary amine.
 16. The composition of claim 15 further characterized in that the tertiary amine is N-methylimidazole.
 17. The composition of claim 1 further characterized in that compounds (i), (ii), (iii) and (iv) are each present at a level to provide about 0.05 to about 3.0 acid groups and about 0.5 to about 4.0 epoxy groups and about 0.05 to about 6.0 hydroxyl groups for each anhydride group.
 18. The composition of claim 17 further characterized in that compounds (i), (ii), (iii) and (iv) are each present at a level to provide 1.0 to 2.0 acid groups and 1.0 to 3.0 epoxy groups and 1.0 to 4.0 hydroxyl groups for each anhydride group.
 19. A curable composition which comprises:(i) an acid-functional polymer having an average of at least two carboxylic acid groups per molecule and which is selected from the group consisting of acid-functional free radical addition polymers obtained by the polymerization of unsaturated acids and one or more copolymerizable monomers, and acid-functional polyester polymers, with the proviso that the acid-functional polymers are not obtained by the reaction of a hydroxy-functional polymer and a cyclic carboxylic acid anhydride; and (ii) an anhydride-functional polymer having an average of at least two cyclic carboxylic acid anhydride groups per molecule and wherein the anhydride-functional polymer is the addition polymerization reaction product of (a) 5 to about 40 weight percent of an ethylenically unsaturated monoanhydride and (b) 60 to about 95 weight percent of at least one other ethylenically unsaturated monomer copolymerizable with the ethylenically unsaturated anhydride; and (iii) an epoxy-functional compound having an average of at least two cycloaliphatic epoxy groups per molecule; and (iv) a hydroxy-functional polymer having an average of at least two hydroxyl groups per molecule;with the proviso that none of the acid-functional polymer (i), the anhydride functional polymer (ii), the epoxy functional compound (iii), or the hydroxy functional polymer (iv) are identical to each other.
 20. The composition of claim 19 further characterized in that the anhydride-functional polymer has a number average molecular weight of at least about
 500. 21. The composition of claim 20 further characterized in that the unsaturated monomer having anhydride funelronality is maleic anhydride.
 22. The composition of claim 19 further characterized in that the epoxy-functional compound is selected from the group consisting of 3,4-epoxy cyclohexylmethyl 3,4-epoxycyclohexane carboxylate; 3,4-epoxy 6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexane carboxylate; bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate; bis (2,3-epoxycyclopentyl) ether; dipentene dioxide; 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-metadioxane; and bis(3,4-epoxycyclohexylmethyl)adipate.
 23. The composition of claim 19 further characterized in that the hydroxy-functional polymer has a number average molecular weight of at least about
 400. 24. The composition of claim 23 further characterized in that the hydroxy-functional polymer is the addition polymerization reaction product of (a) 10 to about 60 weight percent of a hydroxy-functional ethylenically unsaturated monomer and (b) 40 to about 90 weight percent of at least one ethylenically unsaturated monomer copolymerizable with the hydroxy-functional monomer.
 25. The composition of claim 19 further characterized in that it also incorporates a catalyst for the reaction of acid groups and epoxy groups.
 26. The composition of claim 25 further characterized in that the catalyst is triphenyl phosphine.
 27. The composition of claim 19 further characterized in that it also incorporates a catalyst for the reaction of anhydride and hydroxyl groups.
 28. The composition of claim 27 further characterized in that the catalyst is a tertiary amine.
 29. The composition of claim 28 further characterized in that the tertiary amine is N-methylimidazole.
 30. The composition of claim 19 further characterized in that compounds (i), (ii), (iii) and (iv) are each present at a level to provide about 0.05 to about 3.0 acid groups and about 0.5 to about 4.0 epoxy groups and about 0.05 to about 6.0 hydroxyl groups for each anhydride group.
 31. The composition of claim 30 further characterized in that compounds (i), (ii), (iii) and (iv) are each present at a level to provide 1.0 to 2.0 acid groups and 1.0 to 3.0 epoxy groups and 1.0 to 4.0 hydroxyl groups for each anhydride group. 